But the limited practical outcomes of the back-to-back meetings with the EU, NATO and G7 also underlined the limited options even closely-aligned capitals have in confronting Moscow.

Meeting the president of the European Council, Charles Michel, Biden stressed that "the single most important thing we have to do in the West is to be united".

President Vladimir Putin, he warned, would try to divide the members of the NATO alliance as the US, EU and allies ramp up sanctions to punish Russia's military aggression.

"He'd rather face 30 independent countries than 30 united countries," Biden said, promising to seek "total and complete unity among the major democracies".

Thus far, beyond rhetorical support for Ukrainian President Volodymyr Zelensky's determined but outgunned government, Western unity has expressed itself through sanctions policy.

Washington, London and Brussels alike have heaped economic penalties on Russia -- while rushing shipments of anti-tank and anti-aircraft missiles to Ukraine's defenders.

But European powers have stopped short of applying measures against Russian gas supplies, fearing the consequences for their own energy security.

And, despite the impressive line-up of leaders at some or all of Brussels's triple-decker, there was little new to report on daring new measures.

- 'Sanctions never deter' -

In any case, the unprecedented array of financial restrictions already applied to Moscow have done nothing to dissuade Putin from shelling Ukrainian cities.

Confronted about this reality by a reporter's question, Biden let his frustration show.

"Let's get something straight," he declared.

"You remember -- if you've covered me from the beginning -- I did not say that, in fact, the sanctions would deter him. Sanctions never deter. You keep talking about that."

The sanctions that the NATO and EU leaders recommitted to, Biden argued, were not meant to head off Russia's invasion but to "increase the pain" on Putin's regime.

"Why I asked for this NATO meeting today is to be sure that, after a month, we will sustain what we're doing," Biden said.

"Not just next month, the following month, but for the remainder of this entire year. That's what will stop him."

The joint statement issued by Biden and the 27 EU leaders reflected this joint determination.

The leaders "reviewed their ongoing efforts to impose economic costs on Russia and Belarus, as well as their readiness to adopt additional measures and to stop any attempts to circumvent sanctions".

A White House official said they expressed "continued support for sanctions and humanitarian assistance, with a strong message of transatlantic unity and the need to stay the course.

"President Biden enjoyed a warm and friendly meeting with EU leaders at their council meeting tonight, where he shook the hand of nearly every leader in the room and spoke longer with several of them."

But, a month into a conflict launched by a Kremlin leader whom Biden has already dubbed a "war criminal", there were no spectacular pledges of tougher action.

Ukraine's Zelensky has pleaded with his European friends to halt oil and gas imports from Russia, which fill Moscow's war chest to the tune of hundreds of millions of dollars per day.

But American officials admit that, while the US is a net energy exporter, and can afford to snub Russian exports, several European allies rely on Russian gas to keep their lights on.

- Chemical red line? -

Practical discussion in Brussels hinged more on preventing Moscow from finding a way to work around previous sanctions by, for example, acting to prevent it liquidising its gold reserves.

Some countries, including Canada, vowed to step up weapons shipments to Ukraine.

But here too the West is limited by what France's President Emmanuel Macron said was the need to ensure that NATO countries are not drawn into the conflict as a "co-belligerent".

Instead, they agreed to create more NATO battle groups based in eastern European countries, to prevent the war spreading beyond Ukraine without intervening in the fighting inside it.

Biden also promised that Washington would have a "response" if Russia deploys chemical or biological weapons -- but could not say what it would be.